If
the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule
13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following
box ☒.

Note: Schedules
filed in paper format shall include a signed original and five copies of the schedule, including all exhibits. See
§ 240.13d-7 for other parties to whom copies are to be sent.

1
The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to
the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided
in a prior cover page.

The information required
on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities
Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject
to all other provisions of the Act (however, see the Notes).

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BIOTECHNOLOGY VALUE FUND, L.P.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

2,163,4481

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

2,163,4481

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

2,163,4481

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

12.1%1

14

TYPE OF REPORTING PERSON

PN

1 Includes 310,194 American
Depositary Shares (“ADSs”), each of which represents one (1) Share.

2

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BIOTECHNOLOGY VALUE FUND II, L.P.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

1,646,1901

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

1,646,1901

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

1,646,1901

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

9.2%1

14

TYPE OF REPORTING PERSON

PN

1 Includes 198,372 ADSs,
each of which represents one (1) Share.

3

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BIOTECHNOLOGY VALUE TRADING FUND OS LP

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

WC

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

CAYMAN ISLANDS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

322,5721

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

322,5721

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

322,5721

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

1.8%1

14

TYPE OF REPORTING PERSON

PN

1 Includes 53,195 ADSs,
each of which represents one (1) Share.

4

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BVF PARTNERS OS LTD.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

CAYMAN ISLANDS

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

322,5721

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

322,5721

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

322,5721

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

1.8%1

14

TYPE OF REPORTING PERSON

CO

1 Includes 53,195 ADSs,
each of which represents one (1) Share.

5

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BVF PARTNERS L.P.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

4,547,6621

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

4,547,6621

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,547,6621

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

25.3%1

14

TYPE OF REPORTING PERSON

PN, IA

1 Includes 625,000 ADSs,
each of which represents one (1) Share.

6

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

BVF INC.

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

DELAWARE

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

4,547,6621

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

4,547,6621

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,547,6621

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

25.3%1

14

TYPE OF REPORTING PERSON

CO

1 Includes 625,000 ADSs,
each of which represents one (1) Share.

7

CUSIP NO. 29604W108

1

NAME OF REPORTING PERSON

MARK N. LAMPERT

2

CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP

(a) ☒

(b) ☐

3

SEC USE ONLY

4

SOURCE OF FUNDS

AF

5

CHECK BOX IF DISCLOSURE OF LEGAL PROCEEDINGS IS REQUIRED PURSUANT TO ITEM 2(d) OR 2(e)

☐

6

CITIZENSHIP OR PLACE OF ORGANIZATION

USA

NUMBER OF

7

SOLE VOTING POWER

SHARES

BENEFICIALLY

- 0 -

OWNED BY

8

SHARED VOTING POWER

EACH

REPORTING

4,547,6621

PERSON WITH

9

SOLE DISPOSITIVE POWER

- 0 -

10

SHARED DISPOSITIVE POWER

4,547,6621

11

AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON

4,547,6621

12

CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (11) EXCLUDES CERTAIN SHARES

☐

13

PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (11)

25.3%1

14

TYPE OF REPORTING PERSON

IN

1 Includes 625,000 ADSs,
each of which represents one (1) Share.

8

CUSIP NO. 29604W108

The following constitutes
Amendment No. 1 to the Schedule 13D filed by the undersigned (the “Amendment No. 1”). This Amendment No. 1 amends the
Schedule 13D as specifically set forth herein.

Item 3.

Source and Amount of Funds or Other Consideration.

Item 3 is hereby amended and restated
to read as follows:

The Shares and ADSs
purchased by BVF, BVF2 and Trading Fund OS were purchased with working capital (which may, at any given time, include margin loans
made by brokerage firms in the ordinary course of business) in open market purchases, except as otherwise noted. The aggregate
purchase price of the 1,853,254 Shares beneficially owned by BVF is approximately $23,816,268, including brokerage commissions.
The aggregate purchase price of the 310,194 ADSs beneficially owned by BVF is approximately $7,215,112, including brokerage commissions.
The aggregate purchase price of the 1,447,818 Shares beneficially owned by BVF2 is approximately $18,307,293, including brokerage
commissions. The aggregate purchase price of the 198,372 ADSs beneficially owned by BVF2 is approximately $4,614,133, including
brokerage commissions. The aggregate purchase price of the 269,377 Shares beneficially owned by Trading Fund OS is approximately
$3,643,823, including brokerage commissions. The aggregate purchase price of the 53,195 ADSs beneficially owned by Trading Fund
OS is approximately $1,237,316, including brokerage commissions. The aggregate purchase price of the 352,213 Shares held in the
Partners Managed Accounts is approximately $4,875,594, including brokerage commissions. The aggregate purchase price of the 63,239
ADSs held in the Partners Managed Accounts is approximately $1,470,939, including brokerage commissions.

Item 5.

Interest in Securities of the Issuer.

Items 5(a)-(c) are hereby amended and
restated to read as follows:

(a) The
aggregate percentage of Shares reported owned by each person named herein is based on 17,940,035 Shares outstanding as of June
30, 2018, as disclosed by the Issuer.

As of the close of
business on November 8, 2018, (i) BVF beneficially owned 2,163,448 Shares, including 310,194 ADSs, representing percentage ownership
of approximately 12.1% of the Shares outstanding, (ii) BVF2 beneficially owned 1,646,190 Shares, including 198,372 ADSs, representing
percentage ownership of approximately 9.2% of the Shares outstanding, (iii) Trading Fund OS beneficially owned 322,572 Shares,
including 53,195 ADSs, representing percentage ownership of approximately 1.8% of the Shares outstanding and (iv) 415,452 Shares,
including 63,239 ADSs, were held in the Partners Managed Accounts, representing percentage ownership of approximately 2.3% of the
Shares outstanding.

Partners OS, as the
general partner of Trading Fund OS, may be deemed to beneficially own the 322,572 Shares beneficially owned by Trading Fund OS,
representing percentage ownership of approximately 1.8% of the Shares outstanding.

Partners, as the general
partner of BVF and BVF2, the sole member of Partners OS, and the investment manager of Trading Fund OS and the Partners Managed
Accounts, may be deemed to beneficially own the 4,547,662 Shares beneficially owned in the aggregate by BVF, BVF2, Trading Fund
OS, and the Partners Managed Accounts, representing percentage ownership of approximately 25.3% of the Shares outstanding.

BVF Inc., as the general
partner of Partners, may be deemed to beneficially own the 4,547,662 Shares beneficially owned by Partners, representing percentage
ownership of approximately 25.3% of the Shares outstanding.

9

CUSIP NO. 29604W108

Mr. Lampert, as a
director and officer of BVF Inc., may be deemed to beneficially own the 4,547,662 Shares beneficially owned by BVF Inc., representing
percentage ownership of approximately 25.3% of the Shares outstanding.

(b) Each
of BVF, BVF2, and Trading Fund OS, shares with Partners voting and dispositive power over the Shares each such entity beneficially
owns. Trading Fund OS, shares with Partners OS, voting and dispositive power over the Shares beneficially owned by Trading Fund
OS. Partners, BVF Inc. and Mr. Lampert share voting and dispositive power over the 4,547,662 Shares they may be deemed to beneficially
own with BVF, BVF2, Trading Fund OS, Partners OS and the Partners Managed Accounts.

(c) Schedule
A annexed hereto lists all transactions in securities of the Issuer during the past sixty days by the Reporting Persons. All of
such transactions were effected in the open market, except as otherwise noted.

10

CUSIP NO. 29604W108

SIGNATURES

After reasonable inquiry
and to the best of his knowledge and belief, each of the undersigned certifies that the information set forth in this statement
is true, complete and correct.

Dated: November 8, 2018

BIOTECHNOLOGY VALUE FUND, L.P.

BVF INC.

By:

BVF Partners L.P., its general partner

/s/ Mark N. Lampert

By:

BVF Inc., its general partner

By:

Mark N. Lampert

President

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

/s/ Mark N. Lampert

MARK N. LAMPERT

BIOTECHNOLOGY VALUE FUND II, L.P.

By:

BVF Partners L.P., its general partner

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

BVF PARTNERS L.P.

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

BVF PARTNERS OS LTD.

By:

BVF Partners L.P., its sole member

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

Biotechnology Value Trading Fund OS LP

By:

BVF Partners L.P., its investment manager

By:

BVF Inc., its general partner

By:

/s/ Mark N. Lampert

Mark N. Lampert

President

11

CUSIP NO. 29604W108

SCHEDULE A

Transactions in the Securities
of the Issuer During the Past Sixty Days